Numerous chemicals encountered in the environment may alter reproductive functions. These studies are aimed at determining where in the male reproductive tract some of these chemicals act, and the mechanisms by which they act. This year, disposition studies were completed for boron (administered as boric acid). The data show that the testis and other potential reproductive target organs (epididymis, brain) do not accumulate boron more than do non-reproductive organs: the reproductive toxicity is not due to selective accumulation by the reproductive system. Additional boric acid (BA) studies examined the development of the lesion, and numerous reproductive parameters, in animals exposed to 3000, 4500, 6000, and 9000 ppm BA in feed. Selected animals from each group were sacrificed weekly for up to 9 weeks. In addition, two control groups are being examined, evaluating if there is a difference In recovery after varying durations of atrophy, and if there are dose-related differences in the ability of the testis to recover. Preliminary data indicate that the lesion reported earlier for 9000 ppm BA is not just a high-dose effect, but occurs at lower concentrations as well. Future studies may examine for possible hormonal involvement after varying periods of exposure.